(a) Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device. More particularly, the present invention relates to a method for forming an interconnection line in a semiconductor device.
(b) Description of the Related Art
Generally, wiring technology refers to a technology for realizing interconnections, power supplying routes, and signal transmission routes in an integrated circuit (IC). Conventionally, aluminum (Al) has been widely used as a line material. However, line resistance and contact resistance has increased as line widths decrease according to trends of higher integration and higher speeds in semiconductor devices. Therefore, copper (Cu) lines have been actively researched for those reasons and to address the problem of electromigration (EM).
Copper shows resistivity lower than aluminum by about 62%, and it shows better strength against electromigration. Therefore, better reliability may be obtained from copper lines especially for a semiconductor device of high integration and high speed.
On the other hand, copper is difficult to dry-etch in comparison with aluminum. Therefore, copper interconnection lines generally have to be formed by a dual damascene process by which a damascene pattern including a contact hole and a trench is formed in an interlayer insulating layer.
Such a conventional method for forming interconnection lines will now be described with reference to FIG. 1A to FIG. 1E. In FIG. 1A to FIG. 1E, only a part of a semiconductor device has been shown in cross-sectional views, and it should be understood that a semiconductor device may include a plurality of parts having the same schematic sectional structure.
As shown in FIG. 1A, lower interconnection lines 12 insulated by a lower interlayer insulating layer 11 are formed on a semiconductor substrate 10. A first etch stop layer 13 and a first interlayer insulating layer 14 are sequentially deposited on such a semiconductor substrate 10. The first etch stop layer 13 has high etch selectivity with respect to the first interlayer insulating layer 14, and it may comprise a nitride layer, e.g., Si3N4. The first interlayer insulating layer 14 may comprise an oxide layer, e.g., SiO2 formed by plasma deposition from a SiH4 source gas.
Subsequently, a contact hole partially exposing the lower interconnection line 12 is formed by sequentially patterning the first interlayer insulating layer 14 and the first etch stop layer 13 by photolithography and dry etching. Then, a photoresist layer 15 is formed on the first interlayer insulating layer 14 so as to fill the contact hole.
Then, as shown in FIG. 1B, the photoresist layer 15 on the first interlayer insulating layer 14 is etched back to the degree that the first interlayer insulating layer 14 is exposed. In this case, the photoresist layer 15 within the contact hole is partially removed such that a recess 16 may be formed at a top thereof.
Subsequently, as shown in FIG. 1C, the second etch stop layer 17 is deposited on the first interlayer insulating layer 14 to fill the recess 16, and then the second interlayer insulating layer 18 is deposited on the second etch stop layer 17.
The same as the first etch stop layer 13, the second etch stop layer 17 may comprise a nitride layer, e.g., Si3N4. The same as the first interlayer insulating layer 14, the second interlayer insulating layer 18 may comprise an oxide layer, e.g., SiO2 deposited from a SiH4 source gas.
Subsequently, a trench 19 is formed by patterning the second interlayer insulating layer 18 by photolithography and etching. The trench 19 has a bigger size (e.g., a larger width) than the contact hole such that the second etch stop layer 17 may be partially exposed at positions above and adjacent to the photo resist 15.
Then, as shown in FIG. 1D, a damascene pattern 20 including the contact hole and the trench 19 is formed by sequentially removing the exposed second etch stop layer 17 and the photoresist layer 15. Then, as shown in FIG. 1E, a copper layer is deposited on the second interlayer insulating layer 18 and in the contact hole by an electroplating method such that the damascene pattern 20 is filled. Although not shown in the drawings, a diffusion barrier may be first formed in the damascene pattern 20 (i.e., on the second interlayer insulating layer 18 and before the copper layer) such that the diffusion of copper into adjacent and/or underlying layers may be blocked.
Then, a chemical mechanical polishing (CMP) process is performed to remove an upper portion of the copper layer such that the copper layer may be divided by the second interlayer insulating layer 18 (i.e., all copper outside of the damascene pattern 20 in FIG. 1D is removed). By such a CMP process, an upper interconnection line 21 contacting the lower interconnection line 12 is formed, and at the same time the top surface is planarized.
A depth of the recess 16 (formed by etching back the photoresist layer 15) influences the photolithography process for forming the trench 19, on which a critical dimension (CD) of the trench 19 depends. Therefore, uniformity in depths of the recesses 16 takes an important role in obtaining sufficient CD uniformity of the damascene pattern 20.
However, a region having high pattern density and a region having relatively low pattern density may show differences in etching speed during etch back of the photoresist layer 15. As a result, the recess 16 is formed deeper in the region having high pattern density as shown in FIG. 2A, and shallower in the region having low pattern density as shown in FIG. 2B. Therefore, a recess depth difference occurs between regions of different pattern densities. Consequently, the CD of the damascene pattern 20 becomes higher in the region having higher pattern density, and CD of the damascene pattern 20 becomes lower in the region having lower pattern density. Such a non-uniformity of CD causes a deterioration of the interconnection lines.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form information that may be already known in this country to a person of ordinary skill in the art.